1. Field of the Invention
This invention relates to reflective roadway markers that are used for traffic lane delineation, in particular, to markers with enhanced reflectivity, impact resistant and low cost.
2. Related Art Roadway markers are adhered to pavements along centerlines, edge lines, lane dividers or guardrail delineators. Other roadway markers are used as temporary lane dividers in temporary constructions, detours or prior to permanent marking of newly paved roadways. Since 1965, the most commonly used reflective roadway markers are based on Heenan U.S. Pat. No. 3,332,327 or Balint U.S. Pat. No. 3,409,344. Typically, this type of markers are produced in a process consisting of four to five steps: First, injection molding of a thermoplastic shell, either integrally molded with the reflective face, or the reflective faces welded on a corresponding open recesses within the shell. The reflective face, having 350 or more cube corner reflective elements on each reflective face of the shell. Secondly, either the cube corner reflective elements within a shell or the entire inside surface of the shell coated with a reflective sealer by a process known as vacuum metalizing. This metallic sealer needed to seal the cube corner reflective elements so they retain part of their reflectivity prior to the next step, of filling the shell with a thermosetting resinous material, such as epoxy or polyurethane.
This resinous filler material encapsulate the metalized cube corner reflective elements and give the marker the structural body. Finally, a layer of relatively course sand or glass beads dispersed over the top surface of the filler material prior to solidification of the filler material.
Part of the sand particles will remain partially protruding above this planar surface of the marker base, thereby increase the adhesive wetting parameter of the base surface. This will improve adhesion to substrate, regardless of the type of adhesive used. This type of markers worked well for six or seven months, however, due to poor abrasion and impact resistant of the thermoplastic shell, nearly 60% of the reflectivity is lost thereafter, Also, since the coefficient of thermal expansion of the shell material and the resinous filler material vary, this causes pealing of the reflective face or the shell from the resinous body, thereby losing reflectivity. Several attempt were made to improve abrasion resistant of the reflective face. One was the thin layer of glass, in U.S. Pat. No. 4,340,319, Another attempt was the use of polymeric coating of the reflective face, as described in U.S. Pat. No. 4,753,548 (Forrer). These abrasion resistant coating proving to be expensive and tend to reduce reflectivity. Other major development in the pavement marker art have been made in the attempt to eliminate the use of the metalized sealer for the cube corner reflective elements. This has been achieved by dividing the inside surface of the reflective face into reflective cells, each cell will have several cube corner reflective elements, the cells isolated from each other by partition and load carrying walls. The entire reflective face welded to corresponding recesses within a hollowed or solid body. This method is disclosed in U.S. Pat. Nos. 4,227,772 (Heenan); 4,232,979; and 4,340,319 (Johnson et al); 4,498,733 (Flanagan). These markers proved to be superior in reflectivity, however, lack of enough adhesive wetting parameter lead to poor adhesion to roadways, hence caused short life cycle for this type of markers. This applicant successfully developed two markers with non-metallized multi-cell reflective roadway. One roadway marker utilizes raised rhombic shaped abrasion reducing and load transferring raised ridges, which act to intercede abrasion elements and impact load, the shell filled with impact resistant epoxy. The marker body having a base with large wetting parameter for shear and flexural strength, as disclosed in U.S. Pat. No. 4,726,706.
The second roadway marker of this applicant, U.S. Pat. No. 5,927,897 developed a mean to increase the abrasion resistant of the reflective face by coating the reflective face with diamond-like film and by having holding pins extended beyond the partition walls into the body, the holding pins sealed by the filler material; this works very effectively, providing structural strength and maximum adhesive wetting parameter. The entire above reflective pavement markers are incorporated herein by reference in their entireties. Applicant present goal to have a roadway marker having: high reflectivity, enhance structural body, abrasion resistant, low cost, marker base area with maximum wetting parameter and very simple yet consistent process to manufacture.